Process of precipitating ulmic compounds from the black liquors of soda pulp-mills.



N. A. LANGLET.

PROCESS OI PRECIPITATING ULMIG COMPOUNDS FROM THE BLACK LIQUORS 0P SODA PULP MILLS.

APPLICATION FILED JULY 30, 1909.

1,062,01 6. Patented May 20, 1913.

w jjnesses lnvenpar' NILS ABRAHAM LANGLET, OF GOTTENBOBG, SWEDEN.

PROCESS OF PRECIPITATING ULMIC COMPOUNDS FROM THE BLACK LIQUORS OF SODA PULP-MILLS.

Application filed July 30, 1909.

To all whom it may concern:

Be it known that I, NILs ABRAHAM LANG- LET, a subject of the King of Sweden, residing at Gottenborg, in the Kingdom of Sweden, have invented a new and useful Process of Precipitating Ulmic Compounds from the Black Liquors of Soda Pulp-Mills, of which the following is a specification.

This invention relates to a process of precipitating ulmic compounds from the black liquors of soda pulp mills.

In order to free the black liquors, obtained in pulp mills at the boiling of wood with lye, from the dissolved dark-colored organic substances arising from the lignin of the wood, different processes of precipitating with acids of various kinds have been more or less successfully employed.

Among suchprocesses it has been proposed to expose the liquors to electrolysis, in which case the acids liberated at the anode cause a precipitation of the ulmiccom-' pounds, said compounds being also in their nature of weak acids concentrated at the anode and precipitated. It has, however, been found that, if a black liquor obtained by the soda process is directly exposed to electrolysis, the whole quantity of ulmic compounds precipitated at the anode, or in the anode chamber, forms a sticky mass which it is almost impossible to filter. The

treating of such black liquors by electrolysis,

processes of regenerating spent liquors from as hitherto performed, is therefore impractical.

The object of the invention is to make i possible to electrolyze the black liquors in such a manner as to precipitate the ulmic compounds in a form in which they may be easily separated by filtration from the mother liquor.

The invention consists in performing the electrolysis under certain conditions hereinafter set forth and pointed out in the claims.

One of the conditions necessary for obtaining a filterable precipitate consists in increasing the salt concentration of the liquor. Inasmuch as the dissolved organic substance is slightly acid and on account thereof occurs in the solution in the form of sodium salts, such an increase of the salt concentration may be effected by merely evaporating the liquor. As it is, however, somewhat diflicult to perform the precipitation in such a concentrated solution of the substances to be precipitated, I preferv to Specification of Letters Patent.

- Patented May 20, 1913.

Serial No. 510,469.

increase the salt concentration by adding salts to the liquor. Since the said salts remain 1n the regenerated liquor, they should be of such a character as to have no unfavorable influence on the boiling of cellulose matters. Such salts are, for instance, the sulfate, the carbonate or the chlorid of sodium, the latter salt being preferred on account of its cheapness and for other reasons.

The precipitation should be performed at a temperature not lower than 65 centigrade, a condition which together with a suitable salt concentration causes the precipitate to be obtained in a fine-grained and easily filterable form.

The electrolysis may be performed in any well known manner. It is preferred to have the electrode chambers separated by a porous partition and to supply the concentrated black liquor to the anode chamber solely,

while the cathode chamber is filled with regenerated soda lye or with a solution of sodium chlorid. This solution may be used until the ratio between the caustic soda formed in the said chamber and the remain ing quantity of sodium chlorid is suitable for boiling cellulose matters id performing the desired precipitation, whereupon the solution may be employed for compensating the losses of alkali in theprocesses.

The invention differs thus from earlier soda pulp mills by electrolysis by this that a filterable precipitate is obtained by means of said invention on account of the electrolysis being performed at elevated temperature and increased salt concentration of the liquor, a filterable precipitate not being obtainable without taking both of said measures.

In order that the invention may be more easily understood, I will now describe in what manner the same may be performed with, for instance, sulfate, reference being had to the drawing which shows an apparatus adapted to be used in carrying the invention into effect. The electrolyzing vessel a contains an anode chamber 6 and a cathode chamber 0 separated by a diaphragm d. The diaphragm (i may be porous and extend to the bottom of the vessel a, or it may terminate at a distance from the bottom of the vessel, as shown in the drawing, in which case the chambers b and a may be separated by a filter f of sand or other suitable material. The liquor g in the cathode chamber 0 may consist of a solution of sulfate or carbonate or hydroxid of sodium, the liquor h in the anode chamber 6 consisting of the black liquor to be treated. The anode i may consist of platinum, carbon or other material. refractory to oxygen, the cathode 7c of iron or other suitable metal. The black liquor h is suitably kept heated above 65 Centigrade, for instance by a hot water spiral tube Z. Before the electrolysis is performed, 10 to 20 per cent. of sodium sulfate (containing Water) may be added to the black liquor. At first the precipitate arising at the anode is dissolved but it becomes permanent shortly and a light (pale) foam shows when the precipitation is completed. The precipitate is separated and the solution is ready (after causticizing and addition of the cathode liquor, if required) to be again used for boiling cellulose substances.

If desired, the precipitation of the ulmic compounds and the separation of said compounds from the liquor may take place simultaneously.

The process may be used for sulfurous lyes but it is more suitable for lyes which do not contain sulfur in which case the use of sodium sulfate is, obviously, to be avoided. The salt concentration necessary for obtaining an easily filterable precipitate is thereby obtained by adding a non-sulfurous salt, such as sodium chlorid, or by concen trating the lye before precipitating, in which case for one thing the concentration of the organic sodium salts is increased, for the other new quantities of salts arise at the the precipitate from the liquor, substantially as and for the purpose set forth.

2. The process of treating black liquors from soda pulp mills, in order to regenerate caustic soda, which consists in adding a sodium salt to the liquor, exposing the said liquor at an elevated temperature, preferably not lower than 65 centigrade, to electrolysis for precipitating in a filterable form dissolved organic substances, and separating the precipitate from the liquor, substantially as and for the purpose set forth.

3. The process of treating black liquors from soda pulp mills, in order to regenerate caustic soda, which consists in adding sodium chlorid to the liquor, exposing the said liquor at an elevated temperature, preferably not lower than 65 centigrade, to electrolysis for precipitating in a filterable form dissolved organic substances, and separating the precipitate from the liquor, substantially as and for the purpose set forth.

NILS ABRAHAM LANGLET. 

